https://forums.linuxmint.com/viewtopic.php?t=358828

 intl.date_time.pattern_override.time_short

  hour - separator - minute - meridian

             h is 12hr   hh is 12hr with leading 0

8:05AM, 12:00noon, 10:14PM

I am running TB 128.7.0esr (64-bit) on Windows 10. Last month(?) the time format for calendar entries changed from 12hr to 24hr. Then I saw that it also changed the time format in mailbox entries. I wanted to go back to 12 hr. After a lot of searching, I FOUND A FIX posted in this Linux forum: https://forums.linuxmint.com/viewtopic.php?t=358828 The time format is specified in a TB preference, intl.date_time.pattern_override.time_short using the Config Editor. Go to Tools - Settings - General. Press the Config Editor button - it is at the bottom of the General section, on the right. In the screen that comes up, enter the preference name: intl.date_time.pattern_override.time_short It shows the current value. On my system it was HH:mm. On the right side, press the pencil icon to change the value per below. When done, press the Check box. THE NEW VALUE WILL NOT TAKE EFFECT UNTIL YOU EXIT AND RESTART TB. The time format is a single stream in 4 parts: hour - separator - minute - meridian Note: No dashes or spaces between the parts. Part 1 - H is 24hr HH is 24hr with leading 0 h is 12hr hh is 12hr with leading 0 Part 2 - separator character. Typically : Part 3 - mm is 2 digit minute Part 4 - bb displays AM/PM/noon. If blank, nothing displayed. I use h:mmbb for 12 hr format with no leading 0, and meridian. 8:05AM, 12:00noon, 10:14PM I believe this will work for all versions on all platforms.